Similarly, he provoked furious indignation when it was revealed he had changed his legal advice about the Iraq war, thereby allegedly allowing his role as government minister to influence his duties as legal advisor.

"Allegations of political bias, whether justified or not, are almost inevitable given the attorney general's seemingly contradictory positions," today's report by the Constitutional Affairs Committee said.

"This situation is not sustainable."

The report said the attorney general's role in the Iraq war, the cash-for-honours affair and the shutting down of the Saudi/BAE corruption investigation had "compromised or appeared to compromise" the role.

Alan Beith, chairman of the committee, said: "Parliament must be able to call to account those who make political decisions in this field, and there needs to be confidence that legal advice and decisions on prosecutions are not being politicised."

The MPs advised separating the political and legal aspects of the roles so that legal advice comes from a career lawyer and the ministerial role is adopted by a Ministry of Justice minister.

Calls for the position to become fully independent resurfaced last year when the government cancelled an investigation into corruption in an arms deal between BAE Systems and the Saudi government.

While it was the attorney general's constitutional role to cancel the investigation on the basis of the national interest, the prime minister's assurance that he took full responsibility led many commentators to believe Lord Goldsmith's role had become all but irrelevant.

Then Lib Dem spokesman on constitutional affairs Simon Hughes said: "It is no criticism of the present attorney general to say that the prime minister's claim that he takes responsibility for the 'no-prosecution' decision has completely undermined the attorney general's constitutional position."

But the most severe blow to the post was the revelation that, after considerable government effort to keep it a secret, Lord Goldsmith had changed his legal advice to the government about the legality of the impending war with Iraq.

In his final advice to the government on March 17 2003, Lord Goldsmith said the use of force was legal under international law and removed the equivocations and doubts contained in his earlier statement.

This led professor Peter Hennessay, of the University of London, to infamously brand him "the most pliable attorney general in recent British political history".